DESCRIPTION: Pregnancy and lactation early in life are associated with a reduced risk of human breast cancer, while pseudopregnancy induced by human chorionic gonadotropin (hCG) has a protective effect against mammary tumorigenesis in rats. The applicant hypothesizes that, by an enhanced gap junction intercellular communication during lactation, the normal mammary epithelial cells can effectively exert influence on a few transformed or premalignant cells. In this application the applicant proposes [Aim 1] that enhanced cell-cell communication induced by hCG modulates genetic alterations in rat mammary glands exposed to NMU; and [Aim II] that enhanced cell-cell communication modulates the genetic alterations in MCF-10 cells and comma-ID cells. In Aim III, he will investigate the transcriptional regulation of the human Cx26 gene by lactogenic hormones or other modulation agents.